Technical Field
The present invention relates to equipment and methods used in subterranean wells and, more particularly, to an expandable tie back seal.
Background Art
Wellbores are typically formed by drilling and thereafter lining a borehole with steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well and the annular area between the outside of the casing and the borehole in the earth is filled with cement to permanently set the casing in the wellbore.
As the wellbore is drilled to a new depth, additional strings of pipe are run into the well to that depth, whereby the upper portion of the string of pipe or liner is overlapping the lower portion of the casing. The liner string is then fixed or hung in the wellbore, usually by some mechanical slip means, well known in the art.
In some instances, wells are completed with the remote perforating of liner to provide a fluid path for hydrocarbons to enter the wellbore where they flow into a screened portion of another smaller tubular or production tubing. In these instances, the wellbore around the tubing is isolated with packers to close the annular area and urge the hydrocarbons into the production tubing. In other completions, the last string of liner extending into the wellbore is itself pre-slotted or perforated to receive and carry hydrocarbons upwards in the wellbore. In these instances, production tubing is usually connected to the to of the liner to serve as a conduit to the surface of the well. In this manner, the liner is “tied back” to the surface of the well.
In order to complete these types of wells, the production tubing is inserted in the top of a liner in a sealing relationship, usually accomplished by the use of a polished bore receptacle in the liner top. A polished bore receptacle has a smooth cylindrical inner bore designed to receive and seal a tubular having a seal assembly on its lower end. The polished bore receptacle and seal assembly combination allows the production tubing to be “stung” into the liner in a sealing relationship and be selectively removed there from. As used herein, the term “polished bore receptacle” refers to a device used to locate and seal a first tubular in a second tubular.
Well-known technology permits wellbore tubular members to be expanded in situ. In addition to simply enlarging a tubular, the technology permits the physical attachment of a smaller tubular to a larger tubular by increasing the outer diameter of a smaller tubular with radial force from within. The expansion can be accomplished by a mandrel or a cone-shaped member urged through the tubular to be expanded or by an expander tool run in on a tubular string. For an example of an expander tool see: U.S. Pat. No. 7,779,910, issued Aug. 24, 2010 to Watson, entitled “Expansion Cone For Expandable Liner Hanger”, which is incorporated herein by reference for all purposes. Additionally, the term “expander tool” is used herein to refer to any member that used to expand a tubular, such as the roller expander tool, a cone member, hydraulic pressure or any other type of expansion member used in the oil and gas industry.
Tie back seals typically incorporate elastomers at the seal interface. Caustic fluids, high temperatures and high pressures encountered downhole often precipitate degradation of elastomeric seals. Degraded seals can develop leaks that can be costly to an operation whether left in place or replaced. When left in place, the quality of a production stream can suffer. When replaced, the cost of equipment and labor as well as costs of lost production, during replacement down-time, will accumulate. Accordingly, there is a need in the art for a highly durable tie back seal without elastomers that provides a reliable seal.